VIENNA, Austria (AP) — The U.N. nuclear watchdog agency said Wednesday that a Syrian site bombed by Israel in 2007 had the characteristics of a nuclear reactor. It also admitted that its investigation into Iran’s alleged nuclear weapons program is deadlocked.

The conclusions were contained in two confidential reports from the International Atomic Energy Agency that were obtained by The Associated Press. The documents were being shared with the 35 nations on the IAEA’s board.

The report on Iran — which also went to the U.N. Security Council — cautioned that Tehran’s stonewalling meant the IAEA could not “provide credible assurances about the absence of undeclared nuclear material and activities.” And it noted that the Islamic Republic continued to expand uranium enrichment, an activity that can make both nuclear fuel or fissile warhead material.

While that conclusion was expected, it was a formal confirmation of Iran’s refusal to heed Security Council demands to freeze such activities, despite three sets of sanctions meant to force an enrichment stop.

Iran denies weapons ambitions, and Syria asserts the site hit more than a year ago by Israeli warplanes had no nuclear functions. But the two reports did little to dispel suspicions about either country.

On Syria, the agency also said that soil samples taken from the bombed site had a “significant number” of chemically processed natural uranium particles. A senior U.N official, who demanded anonymity because the information was restricted, said the findings were unusual for a facility that Syria alleges had no nuclear purpose.

The same official characterized U.N. attempts to elicit answers from Tehran on allegations that it had drafted plans for nuclear weapons programs as at a standstill.

The Syrian report said “it cannot be excluded” that the building destroyed in a remote stretch of the Syrian desert on Sept. 6, 2007, was “intended for non-nuclear use.”

Still, “the features of the building … are similar to what may be found in connection with a reactor site,” it said, suggesting facility’s size also fits that picture.

The report took note of Syrian assertions that any uranium particles found at the site must have come from Israeli missiles that hit the building, near the town of Al Kibar. And it cited Damascus officials as saying the IAEA samples contained only a “very limited number” of such particles.

But the report spoke of a “significant number of … particles” found in the samples.

The senior U.N. official said “the onus of this investigation is on Syria” and noted that the traces were not of depleted uranium — the most commonly used variety of the metal in ammunition, meant to harden ordnance for increased penetration.

Satellite imagery made public in the wake of the Israeli attack noted that the Syrians subsequently removed substantial amounts of topsoil and entombed the building in concrete. But the report also suggested similar activities at three other Syrian sites of IAEA interest.

“Analysis of satellite imagery taken of these locations indicates that landscaping activities and the removal of large containers took place shortly after the agency’s request for access,” it said.

Beyond one visit in June to the Al Kibar site, Syria has refused IAEA requests to return to that location and examine the three other sites, citing the need to protect its military secrets.

In addition, said the report, “Syria has not yet provided the requested documentation” to back up its assertions that the bombed building was a non-nuclear military facility.

On Iran, the document said Tehran had not significantly expanded full or partial operation of nearly 4,000 centrifuges at its cavernous underground facility at Natanz, a city about 300 miles (500 kilometers) south of Tehran. But it said the Islamic Republic was installing, or preparing to install, thousands more of the machines that spin uranium gas to enrich it — with the target of 9,000 centrifuges by next year.

To date, Iran had enriched about 1,400 pounds (630 kilograms) of low-enriched uranium suitable for nuclear fuel, the report said. U.N. officials have said Tehran would have to produce a little more than twice that to begin enriching it to the level needed to produce a nuclear weapon.

Running smoothly, 3,000 centrifuges could produce enough nuclear material for a bomb within 18 months.

Iran denies such plans, saying it wants to enrich for a future large-scale civilian nuclear program. But suspicions have been compounded by its monthslong refusal to answer IAEA questions based on U.S., Israeli and other intelligence.